Magnetic control of high pressure arc lamp



1951 E. J. G. BEESON ETAL 5 5 MAGNETIC CONTROL OF HIGH-PRESSURE ARC LAMPS Filed Jan'. 28, 1948 Invewbov: Eric John Geor g e Beeson, PhiLip Shephevol, b5 CW Theh A c tovneg.

Patented Oct. 16, 1951 MAGNETIC CONTROL ARC L MP Eric J. G. Beeson, Southwell, and Philip Shepherd, Rugby, England, assignors to General Electric Company, a corporation of New York Application January 28, 1948, Serial No. 4,748 In Great Britain February 17, 1947 Claims.

This invention; relates to electric discharge lamps in which an arc discharge is produced in an atmosphere which, during the .operation, is of high pressure and contains the vapor of a vaporizable metal. The invention is particularly applicable in connection with high pressure mercury vapor electric discharge lamps.

As a result largely of convection currents produced in sucha lamp during operation, the arc and the arc flame may be deflected towards and impinge upon the wall of the envelope. If the envelope is of glass, this impingement must be prevented since the heat of the arc would melt the envelope; and even when the envelope is of quartz, this impingement is undesirable inasmuch as de-vitrification of the envelope will occur.

It is well-known to prevent the impingement of the are on the wall of the envelope by means of a magnetic field produced by conveying the operating current to the lamp through the winding of an electromagnet, thefield of which is related to the arc path as to counteract. the deflection. of the arc. Such an arrangement is designed for a lamp required to be used in-a stationary position, the magnetic field being so adjusted that the counteraction of the deflection of the arc is correct for only that one stationary position.

However, for some applications the need arises for a lamp, the angular position of which is varied during operation so that some adjustment of the valueof themagnetic field -is required when the angular position of the lamp is changed. Such a condition arises, forexample, in the case of spotlights'or fioodlamps used inmotion picture studios .and incorporating electric arc discharge lampsas the source of light.

It is an object of the invention to provide'means for automatically adjusting the magnetic fieldas the angular position of the lamp is varied within predetermined limits so as to maintain the strength of the field at the value required for counteracting the tendency of the arc to deflect into contact with the lamp envelope.

According to the invention the object is attained by the use of means .adapted to produce a magnetic field insuch relation to the arc path as to tend to deflect the arc in a direction opposed to its deflection under the action of convection currents within the lamp envelope. The intensity of the field at the arc path is varied with a change in the angular position of the lamp by gravity controlled means so as to maintain the intensity of the field atthe arc path at a value sufiicient to counteract the arc deflection within predetermined limits sci angular position.

OF HIGH PRESSURE A The gravity control means may operate to control the intensity of the magnetic field at the arc path in alternative ways. According to one method the magnetic field-producing means is maintained at a fixed position with relation to the lamp and the arc path and the gravity control means is arranged to vary the position of a magnetic shunt with respect to the magnetic field-producing means as the angular position or" the lamp is varied, the intensity of the field at the arc path being reduced when the magnetic shunt is in closer relation to the magnetic fieldproducing means by by-passing more of the field through the magnetic shunt, whereas when the magnetic shunt is moved away from the magnetic field-producing means less of the field is shunted and the intensity of the field at the arc path is greater. In another arrangement, the gravity control means is arranged to vary the position of the magnetic field-producing means with relation to the arc path so that the intensity of the field is thereby controlled.

The magnetic field-producing means may be in .the form of an electromagnet or a permanent magnet.

The gravity control means is conveniently in the form of a pendulum, the pivotal axis of which is parallel with the axis about which the tilting movement of the lamp is effected. The pendulum is thus arranged to control the position of the magnetic shunt with relation to the field-producing means or tocontrol the movement of the fieldproducing means towards or away from the lamp as the lamp is tilted. In the latter case, the pendulum may operate through the intermediary of a cam and bell-crank lever provided with a fixed pivot, the angular rotation of the cam, caused by the tilting of the lamp being arranged to displace the bell-crank lever and thereby effeet the displacement of the field-producing means, whereby to control the field intensity at the arc path. Obviously, any suitable gravity controlled means maybe utilized to control the position of the shunt or the position of the fieldproducing means with relation to the lamp.

To enable the nature of the invention to be madeclear it will now be described with reference to the accompanying diagrammatic drawings, in which Figs. 1 and 2 show, in end view and elevation, respectively, one arrangement in accordance with the invention with the lamp of Fig. 1 shown in a section taken along the line l-l of Fig. 2 Fig. 3 an end view of an alternative arrangement; Fig. 4 is a wiring diagram including the lamp of Fig. 1 and the coil of an electromagnet connected in series, and Fig. 5 is a view similar to Fig-1 3 showing two electromagnets mounted on opposite sides of a double ended lamp.

Referring firstly to Figs. 1 and 2, we have shown the arrangement as applied to the automatic arc control of a high pressure mercury vapor arc discharge lamp I, having a spherical quartz envelope, a cathode 2 and an anode 3, the cathode and anode being supported by lead-in wires 4 extending through stems 4' projecting in parallel relation from the sealed envelope. The lamp operates at a vapor pressure in the order of atmospheres and the arc discharge is constricted by the pressure of the gaseous atmosphere. The magnetic field-producing means comprises a coil 5 and a core 6 co-axially arranged, the coil 5 being supplied with current from a suitable source which is preferably that supplying the operating current to the lamp; the coil may carry the load current to the lamp as shown in Fig. 4, if desired.

The lamp is intended to be supported in a suitable housing or lantern which is arranged for tilting in the clockwise or anti-clockwise direction, as indicated by the arrows A and A", about a horizontal axis passing through the center of the arc path and normal to said path and a plane including said leads 4. The magnetic field produced by the coil 5 and core 6 is so arranged by adjusting the value of the current in the coil, the number of turns thereof, and the position of the core with relation to the lamp, that when the lamp is tilted in a clockwise direction to its fullest extent the magnetic field is sufficient to counteract the tendency of the arc to bow outwardly into contact with the Wall of the envelope of the lamp under the action of convection currents caused by the heat of the arc in the vapor in which it operates. If then the magnetic field were of constant value when the lamp is tilted into the position shown in Fig. .2 the field would 1 be greater than is necessary to counteract the tendency of the arc to bow under the action of convection currents and would bow it in the reverse direction causing the arc to impinge on the seals and lead-in wires to the electrodes. According to the invention we provide means for reducing the intensity of the magnetic field under these conditions by means of a magnetic shunt 1 in the form of a yoke co-operating with the parts of the core 6 which extend beyond the ends of the coil 5. The yoke is pivotally mounted at 8 and has attached to it a pendulum 9 which remains in the vertical position when the lamp is tilted. In the position shown in Fig. 2 the yoke thus serves to by-pass some of the fiux produced in the core 6 and reduce the intensity of the field available at the arc path. In the event that the lamp is tilted in the anti-clockwise direction from the position shown in Fig. 2, the shunt 1 comes more closely into engagement with the ends of the core 6, still further shunting the magnetic field and reducing its intensity at the are path. The yoke is provided with cut away portions, indicated at H], shaped to provide the" desired shunting effect of the yoke on the core. If the lamp is tilted in the anti-clockwise direction, the requisite magnetic field for counteracting the upward bowing of the arc is provided by the U-shaped circuit formed by the parallel lead-in conductors 4 to the electrodes 3 and 2 and the are between them, as disclosed in British application No. 14,025/45.

In the alternative arrangement shown in Fig. 3 similar parts have been indicated by the reference numerals assigned to them in Figs. 1 and 2. In this arrangement the coil 5 is fixed and the core 6 is made movable axially Within the coil in order to adjust its position with reference to the arc path and thus control the intensity of the field at the are for different angular positions of the lamp.. This is effected by providing the pendulum 9 with a cam ll engaging with one arm of a bell-crank lever 12 mounted on a fixed pivot I3, the other arm M of the bell-crank lever being connected with the core 6. The bell-crank lever is maintained in engagement with the cam H by means of a spring I5.

In this arrangement, as the lamp is tilted the cam rotates angularly with reference to the bellcrank lever I2 and its shape is such as to move the arm I2 of the bell-crank lever and consequently to control the intensity of the field and the arc path.

The desired control of the magnetic field intensity at the arc path is effected by the arrangements described with reference to the drawings within an angular movement of approximately 90 indicated by the chain dotted lines B.

Where a normal or double ended type of lamp is used, i. e., where the electrode leading-in wires enter the bulb on opposite sides, then two mag netic field-producing devices may be used on opposite sides of the lamp, Fig. 5, and having opposite polarity. As the lamp is tilted through the vertical backward and forwards, the fiux from each coil is alternately short-circuited by the magnetic shunts 7.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a support pivoted on a horizontal axis for angular movement within predetermined limits in a vertical plane, a high pressure are discharge device having a straight path between its electrodes mounted on said support for movement therewith, magnetic field producing means also mounted on said support with its field directed so as to counteract in one of the two possible directions the tendency of the arc to bow out of the straight path under the infiuence of convection currents when said path is at its maximum angle to the vertical, and gravity controlled means having an axis of rotation and being mounted on said support with its axis of rotation parallel to the pivotal axis of the support and being coupled with said magneticfield producing means to change the intensity of the magnetic field in said device in direct proportion to the change in angular distance of the straight path from the vertical as the support is so moved around its horizontal axis that the straight path in the device is tilted from the vertical in the direction in which bowing of the arc is counteracted by the magnetic field whereby the arc is maintained in the straight path between said electrodes when the said support is so moved.

2. The combination according to claim 1 wherein the gravity controlled means comprises a pendulum having its pivotal axis parallel with the pivotal axis of the support. 1

3. The combination according to claim 1 wherein the gravity controlled means comprises a pendulum having a pivotal axis parallel with the pivotal axisof the support and a magnetic shunt juxtaposed to said magnetic field producing means and mechanically connected with said change the intensity of .the field. produced .by

said field producing means as the support is moved around its axis.

4. The combination according to claim 1 wherein the gravity controlled means comprises a pendulum having a pivotal axis parallel with the pivotal axis of the support, and a mechanical connection between said pendulum and said field producing means whereby the latter is moved relative to said device as the support is moved on its axis.

5. The combination according to claim 1 wherein the device is mounted on the support with the straight path between its electrodes vertical in an intermediate position of said support and wherein the magnetic field producing means and the gravity controlled means coupled with said magnetic field producing means are in the form of two duplicate units mounted in opposing positions with respect to said device and on said support with the magnetic field producing units being of opposite polarity with respect to each other whereby the arc is maintained in the said straight path when the said path is tilted in either of the two possible directions from the vertical by movement of the support around its horizontal axis. ERIC J. G. BEESON. PHILIP SHEPHERD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 743,237 Bremer Nov. 3, 1903 933,769 Little Sept. 14, 1909 2,027,384 Kenty Jan. 14, 1936 

